This invention relates to electron beam apparatus and more particularly, but not exclusively, to laser apparatus which includes the use of an electron beam.
It is known, for example as described in U.S. Pat. No. 4,698,546, issued Oct. 6, 1987 to Arthur Maitland et al., that an electron beam may be formed in a device comprising an anode and cathode arranged within a gas filled envelope, the cathode having a hole in a surface and, except for the area within the hole, being substantially covered by a layer of insulating material. An electron beam is obtained on application of a suitably large potential difference between the anode and the cathode when a gas discharge is formed. The electron beam originates from within the hole and emerges from the hole in a direction which is normal to the metal surface of the cathode in which the hole is located.